Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method of performing communication based on hybrid beamforming in a wireless communication system, and an apparatus using the same.
Related Art
Methods for supporting a higher data transmission rate have been studied for a wireless communication system to satisfy a steadily increasing demand for wireless data traffic. As one of these methods, a beamforming-based base station employing a wide frequency band of a millimeter wave (mmWave) band is used, expecting a drastic increase in capacity of the cellular system.
Meanwhile, to transmit a plurality of pieces of information to a single user or multiple users, a Multi Input Multi Output (MIMO) system, which is considered in the existing Long Term Evolution (LTE)-Advanced standard, has multiple digital paths or radio frequency (RF) chains. When MIMO communication is performed using these multiple digital paths, a performance gain, such as a diversity gain or multiplexing gain, may be obtained. However, when the number of digital paths is increased to obtain a higher gain, issues about synchronization between digital paths, costs, and operational complexity may arise.
A millimeter wave band system may offset the disadvantage of path attenuation by a beamforming gain using a large number of physical antennas. However, in the existing MIMO system, a digital beamforming technique involves one RF chain for one physical antenna and thus needs a large number of RF chains, which causes problems of costs and operational complexity. Thus, a hybrid beamforming system using digital beamforming and analog beamforming at the same time may be considered for efficient communication in a millimeter wave band. Analog beamforming may form a narrow beam by connecting an array of a plurality of physical antennas to one RF chain and using a phase shifter. As compared with digital beam forming, analog beamforming is inferior in bam sharpness and flexibility in directional adjustment, but has low implementation costs and low complexity due to no increase in the number of digital paths. A hybrid beamforming system resulting from an appropriate combination of advantages and disadvantages of digital beamforming and analog beamforming may be considered in order to efficiently obtain a high communication capacity in a millimeter wave band.